Combined water electrolysis and 2D hydron separator for enhanced hydrogen isotope separation

[Display omitted] •Monolayer graphene boosts H/D and H/T separation in PEM electrolyzers.•Conductivity ratio of H+/D+ in monolayer graphene is ∼ 2.•Graphene increases the differences in H/D conductivity in proton exchange membrane.•Highest H/T separation factor of 14.3 achieved at room temperature.•Operating temperature impacts H/T separation more than time or concentration. This research presents the fabrication and analysis of a graphene/Nafion composite membrane designed to enhance the hydrogen separation performance of a water electrolyzer by leveraging the isotope effect in hydron transport through monolayer graphene, serving as a 2D hydron separator. The composite membrane exhibits lower proton conductivity than a Nafion membrane, leading to a 12 % decrease in water electrolysis cell efficiency at 75 °C. However, the incorporation of monolayer graphene substantially enhances the hardness of the membrane by a factor of 1.38, as measured by nanoindentation. The addition of monolayer graphene also increases the activation energy required for through-plane conduction of H+ and D+, with the graphene itself showing a twofold higher conductivity for H+ over D+. In electrolysis cells containing the composite membrane, the H/D and H/T separation factors improved by approximately 1.4 and 2 times, respectively, compared with those of a Nafion membrane, with a maximum H/T separation factor of ∼ 15 at 15 °C. Although increases in temperature reduce the separation factor, the operation time and the concentration of heavier isotopes in the feed water were found to minimally affect the separation efficiency.